DOL starting 3 Ph Motor and an RCD

[lewlec]

lewlec,
Almost certainly due to high earth leakage by design of the drives rather than by any faults though.

yes.... agreed.

 

[silva.foxx]

@ Gerard

Did you try decreasing the switching frequency?

Have you tried taking the VFD out completely?

.

 

[gerard]

No - the frequency has to remain constant for this application. Didn't try taking it out either.
As discussed previously in this section, I think the VFDs might be on the small side - this is not helping the situation either. Will try the 300mA RCD and see how it goes.....

 

[silva.foxx]

No - the frequency has to remain constant for this application. Didn't try taking it out either.
As discussed previously in this section, I think the VFDs might be on the small side - this is not helping the situation either. Will try the 300mA RCD and see how it goes.....

No, not the output frequency... I said the switching frequency.

By taking out the inverter you can find if the RCD still trips, which can point to another issue, perhaps.

Is the inverter good?

Has this machine ran at all since you've had it?

.

 

[gerard]

No, not the output frequency... I said the switching frequency.

By taking out the inverter you can find if the RCD still trips, which can point to another issue, perhaps.

Is the inverter good?

Has this machine ran at all since you've had it?

.

I increased the ramp times to as much as I could. How do you mean take the inverters out - then nothing would happen? The inverters are good except as I said they might be a bit on the small side and at their max in terms of current capabilities. Yes, the machine is running fine with no problems except it's RCDless!

 

[silva.foxx]

Take a look at page 86, parameter P297... switching frequency. Decrease it. I have seen in IMO manuals that switching freq. contributes to RCD tripping.

I must be on another planet.

Of course taking the inverter out... nothing would happen... just like taking your chain off your motorbike! You wouldn't ride the bike (machine) without it, would you? But you may prove something is not wrong with your engine, clutch and gearbox.

You've stated that the inverter is the definite cause of the RCD tripping, yet have you proved it really?

You've replaced/removed the socket RCD. The machine is running. Why fit an RCD at all now then?

Why is a 30mA RCD fitted? Additional personal protection?

Will a 300mA give this protection? Is 50mA the fatal limit to keep below?

 

[Knobhead]

Right from the outset I’ve wondered why you need an RCD? But I know management can be funny in some plants with socket outlets. If it has to be on a plug and socket then there’s the old fashioned earth proving units. They served us well for decades. The plugs and sockets are still available.

 

[gerard]

I don't think I would gain anything from removing the VFD. It works fine and I'll just have to fine the best solution possible. In an ideal world there would be an rcd protecting the machine. At the moment the machine is well grounded and if I can add any type of rcd I will. Maybe a 300mA is better than nothing?

 

[Knobhead]

I wasn’t suggesting the removal of the VSD but a rethink of the earth protection.

 

[gerard]

It's probably the best idea